Traditional cap designs are often poorly ventilated. Even with mesh in the crown, the wearer's head is still likely to become uncomfortably warm. What is needed is a cap design to promote evaporative cooling of the user's head. Furthermore, traditional cap designs often require an adjustment strap to permit the cap to be used by wearers having different head sizes. What is needed is an adjustable cap that can be slipped on and off, yet proved a snug fit for a variety of wearer head sizes.